1. Field of the Invention
The present invention relates to an exhaust apparatus for a transverse engine which is transversely placed in an engine compartment at a front of a vehicle to allow a cylinder arrangement direction to be oriented in a widthwise direction of the vehicle (vehicle-widthwise direction).
2. Description of the Background Art
Heretofore, this type of transverse engine has been widely known. Typically, an exhaust apparatus for the transverse engine is disposed on a vehicle-rear side of the engine (see, for example, JP 2008-260472A, this document will hereinafter be referred to as “Patent Document 1”). The exhaust apparatus has a plurality of branch pipe portions each communicated with a respective one of a plurality of cylinders of the engine, wherein the branch pipe portions are merged to finally form a single collector pipe portion. Specifically, in the Patent Document 1, the entire cylinders (four cylinders) are divided into a plurality of cylinder groups each consisting of two or more cylinders whose exhaust strokes are not successive with respect to each other (a cylinder group consisting of the first (#1) and fourth (#4) cylinders, and a cylinder group consisting of the second (#2) and third (#3) cylinders), and the branch pipe portions communicated with respective ones of the cylinders in each of the cylinder groups are merged on a cylinder group-by-cylinder group basis to form a plurality of (two) intermediate collector pipe portions. Then, the two intermediate collector pipe portions are merged together to form a final collector pipe portion.
In late years, with a view to reducing exhaust gas emissions during engine warm-up (when an engine is in a cold start mode), an exhaust gas-purifying unit has been provided on a relatively upstream side of an exhaust gas stream to quickly raise a temperature of a catalyst in the exhaust gas-purifying unit. In the Patent Document 1, an exhaust gas-purifying unit (manifold catalytic converter) is provided in each of the intermediate collector pipe portions.
Meanwhile, in view of enhancing engine exhaust efficiency to increase engine output power, it is desirable to maximize a length of each of the branch pipe portions and the intermediate collector pipe portions. From this viewpoint, the exhaust apparatus in the Patent Document 1 is also designed to increase a length of each of the branch pipe portions and the intermediate collector pipe portions. For this purpose, the two intermediate collector pipe portions are disposed inside a tunnel portion formed in a vehicle-widthwise central region of a floor panel.
However, in order to allow the two intermediate collector pipe portions to be disposed inside the tunnel portion, it is necessary to increase width and height dimensions (cross-sectional area) of the tunnel portion. Particularly, in the Patent Document 1, due to the exhaust gas-purifying units provided in the intermediate collector pipe portions, the cross-sectional area of the tunnel portion needs to be further increased. Thus, there remains the need for improvement in view of ensuring a passenger compartment space as widely as possible. Moreover, in the arrangement where the exhaust gas-purifying unit is provided inside the tunnel portion, a traveling wind produced by traveling of a vehicle is more likely to touch the exhaust gas-purifying unit, so that it becomes difficult to quickly raise a temperature of a catalyst in the exhaust gas-purifying unit during engine warm-up. In this regard, there also remains the need for improvement.